1. Field of the Invention
The present invention relates to monolithic multilayer chip inductors. More particularly, the present invention relates to monolithic multilayer chip inductors using combinations of different coil layers to obtain a desired number of coil turns.
2. Problems in the Art
Typical prior art ultra thin inductors consist of two types. One type requires core assembly by the users, such as planar inductors where the coil is part of the printed circuit board. The second type is a planar inductor which is usually fragile and requires manual placement.
One problem encountered with the prior art chip inductors is caused by the expansion and contraction of a circuit board and inductor resulting from a change in temperature. When the ambient temperature changes, materials will expand or contract. Different materials expand and contract at different rates, depending on their coefficient of expansion. Since the coefficients of expansion of a circuit board and a chip inductor are different, the circuit board and chip inductor will expand and contract at different rates causing mechanical stresses on the ceramic component and on the circuit board to which it is soldered.
Another problem encountered in the prior art results from the demand for increasingly small sizes of components. For example, components to be mounted to a printed circuit board used in a PCMCIA card must be very thin. Various problems can result from reducing the size of a component. For example, as the size decreases, the electrical properties, reliability, and cost of prior art components is degraded.
Another problem with certain prior art chip inductors is the lack of versatility during the manufacturing process. Chip inductors are typically manufactured using several layers of coil patterns, including top, bottom, and intermediate layers. Each coil layer has connection ends corresponding to connection ends of the coil above and below it which are electrically connected to make a continuous coil. To determine the number of turns in a finished inductor, manufacturers change the number of intermediate coil layers positioned between the top and bottom layers, leaving the top and bottom layers the same. As a result, in order to line up the connection ends of each coil to make an electrical connection with the corresponding connection ends, two intermediate coil layers must be added at a time. This results in an inefficient use of coils as well as an increased thickness of the chip component. In addition, depending on the number of turns in each coil layer, the number of coils in the finished inductor can only be altered in relatively large increments.